From ECR...
"We have talked to every ECU rebuilder we can find and no one will touch it. If you know of a company that can handle printed circuit repairs, and is willing to do something out of the ordinary, please drop us an email. If we can get these units rebuilt it will help everyone with a 1997 NAS 90."

The infamous, to me at least, MFU (Mighty Fucked-up Unit). I don't know about Defenders, but both of my 95 D1's have failed on the rear wipe/wash and at least one of them on the cruise. On both they switch a ground on/off. I suspect they did it that way to allow multiple circuits from one fuse on light gauge wire, less amp draw on the circuit at switch closure. On an AC circuit it would be analouges to inrush. As far as finding anyone to fix them, good luck, you would probably have better luck finding some one to reverse engineer a replacement.

How? None of the inputs or outputs for the cruise control go through the mfu.

I should have been more precise. The cruise power on one shorted taking everything on fuse 18 with it, that power circuit also feeds rear wipe wash. The MFU also got at least partially smoked at the same time. Not a big deal on that truck, it is a 300TDI conversion so the cruise was abandoned anyway. I had to wire past all the fuse 18 power wiring due to inaccessible burned up wiring.
on the other one, stock 3.9 auto, the rear wiper doesn't work but wash does. Loss of ground through the MFU.
Once you get to the point of having problems with it, there is just a level of complexity that makes solving some problems pretty tuff.